The cliché of the season is that Americans are war-weary from our long slogs in Iraq and Afghanistan. That is true, but not the whole story. To be sure, nothing has done more to discredit an activist foreign policy than the blind missionary arrogance of the Bush administration. But the isolationist temper is not just about the legacy of Iraq. Economic troubles and political dysfunction have contributed to a loss of confidence. Add to the mix a surge of xenophobia, with its calls for higher fences and big-brotherly attention to the danger within. (These anxieties also helped give rise to the expanding surveillance state, just as nativism in that earlier period gave license to J. Edgar Hoover’s obsessive eavesdropping.)

Isolationism is strong in the Tea Party, where mistrust of executive power is profound and where being able to see Russia from your front yard counts as mastery of international affairs. But sophisticated readers of The New York Times are not immune, or so it seems from the comments that arrive when I write in defense of a more assertive foreign policy. (In recent columns I’ve advocated calibrated intervention to shift the balance in Syria’s civil war and using foreign aid to encourage democracy in Egypt.) Not our problems, many readers tell me.

Isolationism is not just an aversion to war, which is an altogether healthy instinct. It is a broader reluctance to engage, to assert responsibility, to commit. Isolationism tends to be pessimistic (we will get it wrong, we will make it worse) and amoral (it is none of our business unless it threatens us directly) and inward-looking (foreign aid is a waste of money better spent at home).